One of the main aspects related to structural materials—such as steel, wood, and concrete—is the capability of measuring how the materials will behave under loading. If a material will be used in structural members under compression, the material has to be tested in order to assess how it will behave under compression; if a material will be applied in structural members under bending, a way of measuring the material behavior under bending has to be conceived and used.
Structural materials—such as concrete—are used in structural members acted upon by loadings that will create compression, tensile stresses, bending, shearing stresses, and torsional stresses. Currently, there exist several tests that can be used to test concrete, mortar, and other cement-based materials under compression and bending. For shearing stresses, interface shear in bonded concrete, and helical tensile stresses due to torsional stresses, though, there is no device, method or apparatus to test concrete.
FIGS. 1A through 4B show the tests currently used to assess concrete strength. (1) The first test is the compression test that measures compressive strength of concrete; this test is standardized in the USA—ASTM C39/C39M Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens—and in several other countries. (2) The second test is the split tension test used to measure tensile strength of concrete; the method is also standardized in the USA—ASTM C496/C496M Standard Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens—and in other countries. (3) The third test measures flexural strength, or bending strength, of concrete; this test is also defined according to standard procedures in the USA: ASTM C78/C78M and ASTM C293/C293M. (4) The fourth test is referred to as Iosipescu shear test and, although the test is not standardized for concrete, it has been used to measure concrete shear strength; the test is standardized to test composite materials (ASTM D7078/D7078M—Standard Test Method for Shear Properties of Composite Materials by V-Notched Rail Shear Method). In all four tests, a universal compression testing machine is used to apply the vertical load downwards.
The inability to assess shear stresses, helical tensile stresses, and shear interface bonding in plain concrete or cored specimens has been a concern of concrete researchers for decades, and the subject is very important to analyze concrete strength and behavior in structural members, and also to evaluate concrete bonding in concrete interfaces. What is needed then are devices and methods for testing concrete shear strength, concrete tensile strength, and concrete shear bonding using torsional stresses in a specimen, for example and without limitation, a cylindrical concrete specimen, or a cored cylinder extracted from a concrete structural member.